The present invention relates to dot matrix printers and, more particularly, in a dot matrix printer of the shuttle variety wherein a plurality of printheads are disposed across the width of a shuttle which is oscillated from side to side within a printer base, to the improvement comprising, the shuttle being disposed within a ballistic energy transfer device mounted for oscillating movement from side to side in the opposite direction to the instantaneous movement of the shuttle; first spring means operably connected between the ballistic energy transfer device and the shuttle for exerting a rebounding force against the shuttle to aid it in reversing direction; and, second spring means operably connected for exerting a centering force against the ballistic energy transfer device.
Dot matrix printers have provided a simple and economical apparatus for computer-driven printing. In a dot matrix printer, a printhead such as that labelled as 10 in FIGS. 1 and 2 has a magnetic drive unit 12 connected to a print face 14 such as those shown by way of example in FIGS. 3 and 4. One or more print pins 16 are connected between the drive unit 12 and the print face 14. For example, FIG. 3 depicts a single print pins 16 while FIG. 4 depicts twelve print pins 16 configured in a 3.times.4 matrix. A print ribbon (not shown) is disposed between the print face 14 and the writing paper upon which printing is to take place. When the magnetic drive unit 12 pushes the pin(s) 16 out of the print face 14, the end(s) push the print ribbon against the paper causing a dot to be printed. Dot matrix printers are powerful in capability since they can produce both text (i.e. alpha-numeric characters) and graphics as a matrix of dots on the page. The process is depicted in FIGS. 5-7. The printhead 10 is moved back and forth transversely over the paper 18 as the paper is moved vertically under the support bar 20 carrying the printhead 10. The printhead 10 and paper 18 are moved by apparatus well known in the art which is, therefore, not shown for simplicity. Likewise, the magnetic drive unit 12 is activated under computer control in a manner well known to those skilled in the art which requires no further explanation. The printhead 10 is moved across the bar 20 from a starting position at the left side of the paper 18 as shown in FIG. 5 to the opposite side of the paper 18 where it reverses direction as depicted in FIG. 6. It continues across the paper in the opposite direction as depicted in FIG. 7 until it reaches its starting point once again. The process then repeats. As the printhead 10 moves across the paper 18, the magnetic drive unit 12 is activated to create one or more lines of dots (depending on the number of print pins 16) which comprise the graphics and/or text 22. The more pins 16, the fewer passes of the printhead 10 are required.
As with anything else, dot matrix printers are subject to numerous tradeoffs. A printer with only a few pins 16 is simple and inexpensive to build. Typically, these are very slow. A printhead 10 with a greater number of pins will be faster for a given quality; however, the cost is high and the printhead is large. To move the high mass of such a printhead across the paper rapidly and then quickly reverse its direction requires a large and expensive drive mechanism. Even then, there are limitations as to how fast one can make the printhead traverse a wide sheet of paper (e.g. fourteen inches) and then reverse direction.
In commercial printers where cost is not a major factor (as compared to the "home" market), shuttle printers such as that depicted in FIGS. 8-10 have been introduced as an answer to the above-mentioned problems of single printhead dot matrix printers. In a shuttle printer, a plurality of printheads 10 are disposed side-by-side on a shuttle 24. The shuttle 24 is then oscillated or shuttled from side to side a shuttle distance "d" as depicted in the figures. Each head 10 covers only a narrow vertical strip on the paper. For example, with eight printheads 10 as shown in FIG. 10, the shuttle 24 only has to move one-eighth the distance required to traverse the whole width of the paper with one printhead. Typically, the side-to-side movement of the shuttle 24 has been created by a rotating motor 26 driving a crank 28 which, in turn, reciprocates a link 30 connected to the shuttle 24. A position wheel 32 attached to the end of the motor shaft 34 is sensed by a sensor 36 to provide a signal of the position of the shuttle 24 as function of the rotation of the crank 28.
As can be appreciated, while solving some problems, shuttle printers have created problems of their own. Principally, the shuttle 24 with its multiple printheads 10 has a high inertial mass. Thus, it is hard to reverse to create the desired shuttle motion. Additionally, the sensor 36 is inexact since it is at the far end of a chain of additive errors from the shuttle 24 itself. To keep the mass low, shuttle printers have typically employed single pin printheads as depicted in FIG. 3. This, of course, means that many more passes or "shuttles" are required to create a finished "line" of text or the like.
Wherefore, it is an object of the present invention to provide a shuttle printer which is able to quickly reverse directions.
It is another object of the present invention to provide a shuttle printer which operates with larger, multiple pin printheads so as to require fewer shuttle motions to create a line of text or the like.
It is yet another object of the present invention to provide a shuttle printer which can be dynamically adjusted for maximum performance.
It is still another object of the present invention to provide a shuttle printer which does not impart high impact forces from the moving shuttle to the printer base.
It is a further object of the present invention to provide a shuttle printer having a position feedback system for the shuttle which accurately reflects the position of the shuttle.
It is still a further object of the present invention to provide a shuttle printer having low friction in the components whereby to achieve maximum benefit from the driving power.
Other objects and benefits of the present invention will become apparent from the description which follows hereinafter when taken in conjunction with the drawing figures which accompany it.